The present invention relates to the control of a semiconductor assembly line based on the life of certain chemicals used in the fabrication and assembly process. In particular, the expected life of certain lithography photoresists and anti-reflective materials is used to control the fabrication and assembly process.
There exist numerous containers of photoresist and anti-reflective materials (chemical material) with varying expiration dates for tracks in the semiconductor factory. The term xe2x80x9ctracksxe2x80x9d is used herein to refer to the assembly process equipment in a semiconductor factory that produce the semiconductor devices in a step by step process; the term xe2x80x9clotxe2x80x9d refers to one or more semiconductor wafers processed together. The containers of chemical materials have expiration dates on them, but the expiration dates are independent of the tracks and the lots they run. The containers are usually known as NOWPAKs in the semiconductor industry, but any containers containing liquid chemicals can be generally used. (NOWPAK(copyright) is a registered trademark of Now Technologies Incorporated.) This invention is applicable to all processes involving chemicals with expiration dates, irrespective of the types of containers used in the factory. A lot can be classified as an individual wafer or a cassette of wafers containing any number of wafers. When a track runs a specific lot with an expired photoresist or anti-reflective material, it can cause scrap or rework.
There is a need for an automated system attached to a track that will monitor and control the product. This includes stopping production on the track if a critical period or expiration date of the chemical material has been reached. Currently, the tracks do not have any such device that will monitor and control the product in conjunction with the life of the chemical materials. Presently, operators are relied upon to monitor when the containers being used on a set of tracks are nearing their expiration dates and when they have reached or passed their expiration dates.
In a semiconductor factory, the containers of chemicals (containers) are supposed to be checked on a daily basis. This is usually done at the beginning of each shift. The operator is supposed to manually check the expiration date on the containers and contact engineering personnel if the resist or anti-reflective (xe2x80x9cARCxe2x80x9d) material has expired. In the line, most of the photoresists such as CGR, APEX-E and UV2HS and anti-reflective materials such as BARL typically have an expected lifetime of 9 months to 1 year. The actual expiration date is listed on the chemical container by the manufacturer. In most cases, the resist/ARC material would be consumed on the tracks well before the expiration date. Therefore, the operator would never run into an expiration condition for the above mentioned chemicals. However, with certain new resists such as JSR M20G, UV82, M22G, M60G, UVN30, UV110 and UV5HS, and anti-reflective materials such as AR3, AR6 and DUV30, the expected lifetime is 6 months and it is common for these materials to be used right up through their expiration dates. With multiple process tools, using multiple tracks, using multiple resists/ARCs with different expiration dates, and with the current set of controls on the tools, it is not possible to ensure that product is not run on the tracks with expired chemicals. The current set of controls includes operators checking and monitoring the expiration date of chemicals on every track at the beginning of their shift and informing the relevant engineering personnel when a material has expired. These controls help in monitoring the expiration dates of the materials used on the tracks but do not ensure that the materials are not used beyond their expiration dates. There is not a mechanism to notify manufacturing and engineering teams about expiring chemicals for appropriate actions. There is thus a potential exposure to run lots with expired chemicals. This would cause running of the tracks in xe2x80x9cOut Of Compliancexe2x80x9d conditions.
The newer resists and ARC materials have critical periods (typically 2 to 3 days) just before their expiration dates during which various process problems may be anticipated. It has been found that some newer chemicals, such as AR3, that are used for the most critical processes in logic semiconductor fabrication have caused scrap product when used on or beyond its expiration date. It has also been found that using some newer materials, such as AR3, up to 4 days prior to expiration has caused process problems which affect the yield of certain processes such as the gate level in the semiconductors. Some of these levels are very critical in the semiconductor fabrication process; accordingly, the materials used for these processes must be monitored and controlled carefully a week prior to their expiration date.
In accordance with the present invention, a method and apparatus are provided for controlling the use of chemical materials in a semiconductor factory. The control is based upon the relation of certain important dates relative to the useful life of the chemical materials used in the semiconductor fabrication process. These dates include the relationship between the current date with the expiration date, a critical date and a warning date for each chemical used on a particular assembly line.
The expiration date is based upon a date beyond which the chemicals are not to be used in the semiconductor factory process. The critical date is usually no more than 3-4 days before the expiration date. Certain chemicals need more careful monitoring during this critical period. The warning date, usually a week before the expiration date, is used to alert the relevant engineering and production staff that a period of high order of attention on a particular production run is required.
There are four major decision points in the method that are implemented by the apparatus. A first decision point determines if a first date, the xe2x80x9ccurrent date,xe2x80x9d is prior to a second date, a xe2x80x9cwarning date.xe2x80x9d The first date selection process instructs the fabrication process to continue if the current date is prior to said warning date.
If the current date is later than the second date (the warning date) and if the current date is prior to a third date (a critical date), a second data selection circuitry instructs the fabrication process to continue and activates a first call warning circuit.
If the current date is later than the third date (the critical date), and if the current date is later than or equal to a fourth date (the expiration date), a third data selection circuitry instructs the fabrication process to stop and activates a third call warning circuit. If the third selection circuitry determines that said current date is earlier than the expiration date, it activates a second call warning circuit and prompts for a manual override signal to permit the process to continue after the critical date and before the expiration date.
A requeue selection permits the fabrication process to continue if the current date is earlier than the warning date, the current date is earlier than the critical date, or if the current date is earlier than expiration date and the manual override is activated. The requeue selection orders a stopping of the process when said current date is equal to or later than said expiration date or the manual override is not activated.
These and other features and advantages of the present invention will be apparent from the following brief description of the drawings, detailed description, and appended claims and drawings.